Cathode-ray tube



Dec. 21, 1948. L, H-BEDFORD ET AL 2,456,809

CATHODE-RAY TUBE I Original Fil-ed Nov. 30, 1943 MODULATOR MODULATOR INVENTORS 1 88 [,c' e' Herberi' Bed/0rd BY JOIuz/BelL f Eric Miles LqucgS/muo G i torn-Leg Patented Dec. 21 1948 I] N l TED 'S TATES PAT E N T "O F F [CE Leslie IHerbert Redford, London, and John Bell and Eric" Miles LanghamJ-Ted'dington, England, assignors'to A10. Cossor Limited, London, England, 'a"'British"company November 30, 1942 14 LGlaims. 1

This invention relates to excitation circuitsand deflection systems for cathode'ray tubes.

Apparatus according'to the invention comprises a cathode ray tube having a pair of deflector plates, means to excite the final anode of the'gun and all other gun electrodes Whichsubstantially influence the focus with cophased alternating voltage relative to cathode, and means to apply between said deflector plates a cophased alternating voltage, wherebythe focus is maintainedand a deflection is produced proportional to the relative amplitudes of thedefiection voltage and the final anode voltage.

According to a preferredform oftheinvention, apparatus for simultaneously displaying, by means of the co-ordinates'of a-spot position on the screen of a cathode ray tube, the'amplitude'of two cophased alternating voltages relative to that of a third cophased voltage-comprises means to apply said third voltagebetween the cathod'e'and the final anode of the cathode ray tubegun'and to applysuitable fractionsthereof toail other gun electrodes which substantially infiuence'the focus, and means to apply said firsttwo voltages between successivepairs of-defiector plates producing deflection in mutually perpendicular directions.

When the potential of the final anode'of'an electron gun is varied relative to cathode, the focus is maintained if the potentials relative to cathode of *the focussing electrode, and of all other electrodes which influence the focus, are varied'in proportion. IL-therefore, all the electrodes of the gun are'excited with alternating voltages relative to cathode in the same phase, then beam current will flow-during every half cycle while the anodes are positivetocathode and the focus will be substantially correctthroughout these half cycles. Thefocus is not,'however, disturbed by the beam current control electrode and it is'preferred inpracticethat'thisbe maintained negative to cathode so asto suppress the beam for a period at eachend of thehalf cycle. Very satisfactory operation is obtained if these periods of suppression are bothof the order of one-sixth of a cycle, so that'beam'current will flow for the central-one-third of the posltivehalf cycle. This may be effected byholding'the potential of beam current control electrode at "an appropriate direct voltage negative to cathode.

A further refinement which may'be employed alternatively or additionally, however, is to "increase the beam current substantially;duringthe 'fraction of a cycle while itis permitted'to'fiow,

beyond the value which it' wouldatta1n if the beam current control electrode were maintained -at-constantpotential negative relative to cathode.

proportional to the potential difference between apair Of'defiectorplate'S, but is inversely-proportional to the potential difference between the final anode of the electron gun and cathode. 'Wh'en, therefore, an alternating voltage is applied between a pair of deflector plates inphase with the alternating voltage between final anode and "cathode, the spot wh'erethe beam impingesonth'e fluorescent screen is theoretically stationary. Its position is determined by the amplitude of the alternating deflection voltage, assuming that the amplitude of the alternating gun voltage remains constant.

The accompanying drawing shows a circuit diagram of 'a cathode ray'oscillograph'tube arranged for alternating current operation in accordance with the invention.

The cathode ray 'oscillograph tube has a cathode 2, a beam current'control electrode '3,"a

first anode '4, a focusing electrode 5 and a final anode '6. These electrodes together form the electron gun. The electron beam leaving the final-anode 6 passes between'two pairs of electrostatic defiector plates, I, '8 "and 9,1!) which are arranged to produce deflections in mutually perpendicular directions. The beam finally impinges in a spot on the'fiuorescent screen I I.

The exciting and deflection voltages are allderived from the common alternating source I, which may have a frequency of 50 cycles.

Transformer I2, which has its primary-winding I3 connected across source I, is provided with three separate secondary windings I4, 1 5, IS.

The electron gun is excited from winding I 4. One end of this winding is earthedand connected to thefinal anode-6. A potentiometer'll is connectedacross winding I4 and the alternating voltages .for the other electrodes of the gun are derived from tappingsthereon. Thus the'focusing electrode '5 and the'cathode {are connected to tappings I8 and I9 respectively. The first anode 4 is shown as connected directly to the final anode n5; but if the gun is so designed that this first :a'node would ordinarily, with "direct vo'ltage excitation, be excited 'at' a "potential negative with :respect to the ".fina1"',anode; then this firstvanode nating voltage or direct voltage, but it is preferably excited with a combination of both. In the arrangement shown it is excited relative to cathode with an alternating voltage drop derived from potentiometer l1 superposed on a direct This,

voltage established across resistance 2|. resistance 2| is the load of a diode rectifier 22, which is connected through coupling condenser 23 between tapping and the end ofpotentiometer l! remote from earth.

The deflection voltages are derived from secondary winding 5, and their amplitudes are modulated, in accordance with phenomena tobe represented, by modulators 24 and 25 respectively. These voltages are shown as applied asymmetrically to deflector plates 8 and I0, only shift voltages being applied to the opposite plates 1 and 9 These shift voltages, also taking the form .of alternating voltages in phase with those applied to the electron gun, are derived from tappings on potentiometers 26, 21, connected across the secondary winding l5, which has an earthed centre-tap. The deflection voltages may, however, be applied symmetrically, with or without the superposition of shift voltages, if this is preferred.

, The arrangement may be regarded as inherently a demodulator; the two co-ordinates of the position of the spot on the screen represent the amplitudes of the output voltages from modulators 24 and 25. The position is independent exhibiting the modulation on a cathode ray tube excited with direct voltage in the ordinary way,

this system provides, in addition to other advantages, a feature of sense indication. So long as the output voltage from modulator 24 is in phase with the voltage of final anode 6 relative to cath- Iode, the beam will be deflected towards thedeflector plate 8. If, however, the modulation is carried through zero and beyond, so that the output voltage of modulator 24 is in anti-phase with that of the final anode relative to cathode, the deflection of the beam is towards deflector plate 1.

It will be evident that the invention is not limited to use in oscillograph tubes, and the term cathode ray tube is, therefore, to be understood as including beam deflection valves.

This application is a division of application Serial No. 512,402, filed November 30, 1943.

We claim:

1. Apparatus comprising a cathode ray tube having a pair of deflector plates, means to excite the'flnal anode of the gun and all other gun electrodes which substantially influence the focus with cophased alternating voltage relative to cathode, and means to apply between said deflector plates a cophased alternating voltage, whereby the focus is maintained and a deflection is'produced proportional to the relative amplitudes of the deflection voltage and the final anode voltage.

that of a third cophased voltage, which comprises means to apply said third voltage between the cathode and the final anode of the cathode ray tube gun and to apply suitable fractions thereof to all other gun electrodes which substantially influence the focus, and means to apply said first two voltages between successive pairs of deflector plates producing deflection in mutually perpendicular directions.

3. Apparatus according to claim 1, comprising means to suppress the electron beam for periods at both ends of each half cycle when the final anode is positive to cathode.

4. Apparatus according to claim 3, wherein each of said periods of suppression is of the order of one-sixth of a cycle.

5. Apparatus according to claim 3, wherein said suppression means comprises means to apply a direct negative voltage bias to the beam current control electrode.

6. Apparatus according to claim 1, comprising means to excite the beam current control electrode with a further cophased alternating voltage relative to cathode to increase the beam current when flowing. v, 7; Apparatus according to claim 2, comprising means to suppress the electron beam for periods at both ends of each half cycle when the final anode is positive to cathode.

8..Apparatus according to claim 2, comprising means to suppress the electron beam for periods at both ends of each half cycle when the final anode is positive to cathode, each of said periods being of the order of one-sixth of a cycle.

9. Apparatus according to claim 2, comprising means to suppress the electron beam for periods at both ends of each half cycle when the final anode is positive to cathode, said suppression means comprising means to apply a direct negative voltage bias to the beam current control electrode.

. 10. Apparatus according to claim 2, comprising means tojexcite the beam current control electrode with a further cophased alternating voltage relative to cathode to increase the beam current when flowing.

11. Cathode ray tube apparatus comprising a cathode, a beam current control electrode, a focussing electrode, and a plurality of anodes forming anelectron gun for producing an electron beam, two pairs of electrostatic deflector plates for producing deflections of said beam in mutually perpendicular directions, a fluorescent screen on which said beam impinges, and means for impressing cophased alternating current directly'upon all of said electrodes, said current being derived directly from a common source of alternating current.

12. Cathode ray tube apparatus as defined in claim 10 havin means forexciting the beam claim 10 having modulators through which symmetrical deflection voltages are applied to said deflector plates, said modulators deriving current from the common source of alternating current. i

14. Cathode ray tube apparatus as defined in claim 10 having modulators and potentiometers for applying asymmetrical deflection voltages to said deflector plates, a modulated voltage derived from the source of alternating current through a modulator being appliedto one deflector plate of each pair and a shift voltage derived from the source of alternating current through a potentiometer being applied to the other deflector plate of each pair.

LESLIE HERBERT BEDFORD.

JOHN BELL.

ERIC MILES LANGHAM.

REFERENCES CITED The following references are of record in the file of this patent:

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